Monday, August 5, 2013

8/5/13 Report - What Actually Determines How Obects Move On a Beach Or In the Water.

Written by the TreasureGuide for the exclusive use of

Four Lead Objects Used in Illustration.
One thing you often read and hear is that heavier objects sink deeper in the sand and are found deeper than lighter objects.  That is partly true, but there are other factors that are just as important as weight in determining where items will be found.

In the past I've shown examples of extremely heavy things, such as concrete barges weighing hundreds of tons, that were washed up onto shore and were found on the surface of the beach.  Obviously there is something to consider besides weight.

Some people, instead of talking about weight, talk about density or specific gravity.  That is more accurate and more to the point than only talking about an item's weight (a ton of Styrofoam will still float), but there are still other factors besides weight and density that affects where an object will be found on a beach or in the water.  

As I've pointed out in the past, and as I've seen no one else do previously, shape is a very important variable for determining where coins and jewelry will be found.  The amount of surface of the object that the water can push against and the amount of surface area that will contact the surface of the sand are both very important factors.  

A flat thin sheet will be moved more by the water than a round ball of the same material and will also not sink into the sand like a round ball would, for example. 

Finger rings are different from either of those shapes, not presenting much vertical surface for the water to push against and not presenting much surface to contact the sand.

I did an experiment to illustrate how objects of different shapes will be move differently by water.  I took the four lead sinkers shown above and placed them in a line on the sand.   All were one ounce except for the larger of the two disks, which was two ounces.   All had the same density and three had the same weight. 

To simulate a wave, I took a large bucket of water and spilled it abruptly on the objects at roughly a thirty degree angle.

Final Position of the Same Four Objects.
To the left is a picture showing the final position. of the four objects that were previously in a line.  The egg shaped object moved the farthest, followed the the fish-shaped sinker, then the lighter disk, and then the larger disk, which was moved the least by the water.

That is what I would have predicted.

The shapes did affect how much the items were moved by the water  - as much as their weights.  Density was the same.  Notice that the fish-shaped sinker is about the same distance away from the small disk-shaped sinker as the small disk sinker is away from the larger sinker. 

I've talked before about coins being shaped to present more surface to the sand and therefore resist sinking while presenting little vertical surface to the force of the water.  Presenting a low profile to the force of the water, coins generally hug the surface of the sand and linger behind as the sand is moved. 

Sinking in beach sand is as much or more a matter of the sand being moved as it is a matter of the weight of the object forcing itself down through the sand.  I'll demonstrate that some time.

Weight did play a roll.  The heaviest of the two objects of similar shape did move less than the lighter one.

I didn't address sinking in this experiment.  I did another experiment to illustrate that, but didn't catch a good picture of the results so I couldn't really show the results of that experiment.  I wanted to improve the experiment anyway, so I'll do it again and hopefully catch some good photos of what is going on.

In the second experiment, the fish-shaped sinker disappeared into the sand below the two coin shaped objects, while the egg shaped sinker did not sink much.  

There are many variables.  Some I haven't yet mentioned.  They include the surface texture of the object, the texture and compactness of the sand and the various layers, the amount of time the object is exposed to the force of water and the way the water is moving, to name some.

I sometimes refer to the weight of the object in my posts when I actually mean something much more.  It is a convenient shorthand that some readers will accept on face value but which others who have read more of my previous posts I hope will understand is not really meant to be taken literally.

I have a lot more to say about this but am running out of time and want to get this posted today.  I'll therefore follow up on topics like this in the future.

On the Treasure Coast the surf is only one foot today, as expected.  The wind is from the west and the beaches are sandy.

It wouldn't be a bad time to take a dip.   Conditions on the beach aren't very good.

One other note on the wood handle conversion that I talked about a few days ago.   Consider the depth of the water you will generally work in determining how long to make the handle.  Or make a two or three and change them.

Happy hunting,